fix(pty): default TERM for resize probes

Preserve explicit caller overrides, but backfill a sensible default
TERM=xterm-256color when missing or blank in the spawn env. CI often
runs without TERM in the parent process, which makes terminal probes
like 'tput cols' fail before winsize reads.

Salvage of #15278's core code fix only — the test changes conflict
with subsequent test refactors on main that now exercise TIOCGWINSZ
directly instead of via 'tput'.

Co-authored-by: LeonSGP43 <154585401+LeonSGP43@users.noreply.github.com>

hermes_cli/pty_bridge.py

@@ -108,9 +108,14 @@ class PtyBridge:
                     "(or pip install -e '.[pty]')."
                 )
             raise PtyUnavailableError("Pseudo-terminals are unavailable.")
-        # Let caller-supplied env fully override inheritance; if they pass
-        # None we inherit the server's env (same semantics as subprocess).
-        spawn_env = os.environ.copy() if env is None else env
+        # PTY-hosted programs expect TERM to describe the terminal type.
+        # CI often runs without TERM in the parent process, which makes
+        # simple terminal probes like `tput cols` fail before winsize reads.
+        # Preserve explicit caller overrides, but backfill a sensible default
+        # when TERM is missing or blank.
+        spawn_env = (os.environ.copy() if env is None else env.copy())
+        if not spawn_env.get("TERM"):
+            spawn_env["TERM"] = "xterm-256color"
         proc = ptyprocess.PtyProcess.spawn(  # type: ignore[union-attr]
             list(argv),
             cwd=cwd,